Paper and method of making same



Patented Feb. 5, 1935 UNITED STATES PATENT OFFICE PAPER AND METHOD OF MAKING SAME No Drawing. Application April 27, 1932, Serial No. 607,896

13 Claims.

This invention relates to paper containing finely divided porousv filling material, such as diatomaceous earth or the like, and a method of making the same. The invention relates particularly to a paper and process of manufacture in which the concentration of pitch into objectionable agglomerates is minimized.

Paper is commonly manufactured by making an aqueous suspension of prepared wood fibers, beating the fibers in the suspension in a so-called beater, collecting the beaten fibers in the form of a felted sheet on a cylinder or Fourdrinier wire paper machine, and then finishing the sheet, as by drying and calendering. Coloring materials such as dyes are frequently added to the aqueous suspension of fibers. The wood pulp used as the source of the fibers may contain chemically and/or mechanically treated fibers. Thus, the pulp may .consist of ground wood, unbleached sulphite or sulphate pulp, bleached sulphite or sulphate pulp, or other common types, including rag fibers. When the fibers are wood, they may be contaminated by substantial amounts of a sticky or resinous material which is herein referred to 26 as pitch. Thus, ground wood and unbleachedsulphite pulp may contain as much as 1.7 parts by weight of pitch to 100 parts of pulp.

The presence of this pitch in the wood pulp or fibers introduces difliculties in the manufacture of 30 paper .from such raw material and also affects the quality of the finished paper. For example, the pitch, which is apparently loosened from the fibers during the preparation of the fibers and thebeating operation, tends to agglomerate into lumps which may adhere to the walls of the beater, to the Fourdrinier wire, to cylinders, or to otherparts of the paper' making equipment. It is sometimes necessary to clean the walls of beaters as often as three times a week in order to remove the incrustation of pitch. At all times there is the passibility that a lump of the pitch may lodge in the sheet of paper and be flattened out as the paper subsequently passes'over a roll during the finishing operation, the result being an undesirable spot of pitch in the sheet of finished paper.

The problem has been widely recognized and various expedients have been proposed to overcome the difliculty due to pitch. Thus-it has been proposed to fabricate paper from aqueous suspensions of fibers which are kept slightly acid, say at a pH value of less, than 7. The eflfect of acidity upon steel and iron parts of the paper machine is undesirable. Also, there has been proposed the use of a large proportion of inorganic filler, over which, presumably, the pitch may become coated. Thus, there has been used approximately 10% by weight of talc, kaolin or barium sulphate on the weight of the wood pulp. Thereare objections to the use of such large proportions of fillers. Such proportions modify the properties of the paper in a direction that is sometimes not allowable. They affect the opacity and weight of the paper. Also, they may afi'ect the color, as by obscuring the color which it is desired to establish in the paper or by actual adsorption of the coloring material. Thus, a clayey product (bentonite) has been found to adsorb certain dyes and adversely affect the color of a paper containing the dyes.

The present invention makes possible the adequate control or distribution of the pitch in the paper, by the use of a filling material of such effectiveness that the proportion required is so small as not to affect seriously other desirable properties of the paper, such as semi-transparency, lightness in weight, and established color.

The filler that is used in accordance with the present invention should consist of fine particles that are individually porous, chemically inert, 25

non-adsorbent of dyes, and adapted to become associated with the pitch more intimately than wood fibers are so associated.

A filler that has been found to meet these requirements to an admirable degree, and that is the filler preferred at this time, is finely divided diatomaceous earth. Particularly satisfactory results have been obtained with diatomaceous earth that has been submitted to calcination in finely divided form. This calcination evidently increases the ease with which pitch may be associated with or absorbed by the diatomaceous earth during its use in accordance with the present invention or decreases the adsorptive capacity of the earth. Thus, the diatomaceous earth that is used may be a product made by calcining as described in U. S. Patent 1,477,394 to Thatcher. However, such a product may have a color that is not white. A white product of a very high rate of absorption and useful in the present invention is made by calcining finely divided diatomaceous earth in the presence of a small proportion of a chemical adapted to flux clay or produce sintering, as described in U. S. Patent 1,502,547 to Calvert, Dern and Alles.

The calcined product, for example, is submitted to treatment such as milling and air separation, to remove particles of grit and to give particles of size desired. Thus, there may be made a finely divided. air separated product in which the major as measured by the Oden sedimentation test, or a product of which more than half is finer than 10 microns in particle size and, suitably, smaller than 5 microns.

This diatomaceous earth of white color and particles of the size specified is particularly useful in making certain thin papers such as tissue, glacine, or the like. In making thicker papers, there may be used finely divided diatomaceous earth of particle size somewhat larger than described above. Thus, there may be used a white, comminuted product made, for example, as described above and having approximately the following distribution of particle sizes: 41% by weight larger than 10 microns, 58% smaller than 10 microns and larger than 2 microns, and 1% smaller than 2 microns.

Diatomaceous earth "of the kind described has very high absorption power as compared to fillers previously used in paper. As measured by the Gardner-Coleman method for determining oil absorption (Physical and Chemical Examination of Paints, Varnishes, Lacquers and Colors, by Gardener, 1930, pages 89 et seq.), the oil absorption by the calcined diatomaceous earth varies 'from parts to parts by weight of oil for each 100 parts'of diatomaceous earth, the exact figure varying with the degree of fineness of the earth and other properties.

The invention may be illustrated by the manufacture of aprinting paper from unbleached sulphite wood pulp.

The wood pulp is supplied to a paper beater in a customary suspension -in water. pension there is then added finely divided diatomaceous earth that has been calcined in the presence of a small amount of flux, as described in said patent to Calvert, Dem and Alles, and then milled and air separated to produce a material of particle sizes which are largely between 3 and 6 microns in size. The amount of such diatomaceous earth added is suitably not more than 4% and usually /2 to 2% of the dry weight of the wood pulp. A proportion that has been found satisfactory is of the weight of thewood pulp. The optimum proportion of diatomaceous earth to be used with a given pulp may be determined by a few simple test preparations and may be varied in accordance with the percentage of pitch in the pulp fumished to the beater. It is not necessary, for most purposes, to use more than 1 part by weight of diatomaceous earth for 1 part of pitch. Usually to part of diatomaceous earth to 1 part of pitch maybe used with satisfactory results.

While the diatomaceous earth may be added in various ways, the diatomaceous earth should be intimately and thoroughly mixed with the pitch and fibers before the fibers are formed into a sheet of paper. A convenient method of addition of the diatomaceous earth is in the form of a water suspension of the earth. Two parts by To this sus- 1,989,709 part of the material is between 3 and 6 microns,

for the addition of the diatomaceous earth to the suspension and thorough mixing of the earth with the fibers, before the paper is formed from the suspension, by felting the fibers into a sheet. 1 The resulting paper may be of color substantially the same as or lighter than that of the fibers used. There may be used dyes, other coloring materials and/or conventional ingredients, in manufacturing steps that are usual.

Paper made from a fibrous material containing pitch, with the use of diatomaceous earth,

contains the pitch more or less uniformly distributed throughout the paper, so that objectionable concentration in spots is minimized. Also, the paper contains diatomaceous earth substantially uniformly distributed throughout the ill tered fibrous material and intimately associated with the pitch.

While the invention has been illustrated chiefly by reference to the compositions comprising felted wood fibers, pitch, andfinely divided diatomaceous earth, the invention comprises felted organic fibrous material containing finely divided diatomaceous earth or equivalent, inert, porous, finely divided filler material, either with or without pitch, in paper or sheet form.

Thus, the use of finely divided diatomaceous earth in paper serves useful purposes in addition to the control of pitch. For example, diatomaceous earth may be used in paper consisting chiefly of organic fibers, to decrease the rate of combustion of the paper by replacing a large amount of combustible fibers by the incombustible filler material.

Since many variations from the illustrative details that have been given may be made without departing from the scope of the invention, it is intended that the invention should be limited only by the terms of the claims.

What I claim is:

1. A paper comprising felted organic fibrous material and finely divided diatomaceous earth that hasbeen calcined in finely divided form.

2. A paper comprisingfelted organic fibrous material and finely divided diatomaceous earth that has been calcined in finely divided form in the presence of a small proportion of a chemical adapted to .flux an ingredient of the diatomaceous earth.

3. A paper' comprising felted organic fibrous material and finely divided diatomaceous earth of which more than half is finer than 10 microns in particle size.

4. A paper comprising felted organic fibrous material and finely divided, calcined diatomaceous earth of which more than half is finer than 5 microns in particle size.

5. A paper comprising wood pulp, finely divided diatomaceous earth, and pitch intimately associated with the diatomaceous earth.

6. A paper comprising chemically treated wood pulp, finely divided diatomaceous earth, and pitch intimately associated with the. diatomaceous earth.

'7. A paper comprising mechanical wood pulp, finely divided diatomaceous earth, and pitch in-. timately associated with the diatomaceous earth, in the proportion of approximately 1 part by weight of pitch to A to part of diatomaceous earth.

8. A paper containing felted fibrous material, pitch and finely divided diatomaceous earth, the pitch being intimately associated with the diatomaceous earth and distributed substantially uniformly throughout the paper.

9. In making paper from an aqueous suspension of fibrous material and pitch, the improvement comprising intimately mixing finely divided,

diatomaceous earthwith the said suspension and thin formingpaper from the resulting mixture.

10. In making paper from an aqueous suspension of fibrous material and pitch, the improvement comprising intimately mixing finely dividedwt'iatomaceous earthwith the said suspension, whereby the pitch becomes associated with the diatomaceous earth, and then forming paper from the suspension.

11. In making paper from an aqueous suspension of fibrous materials and pitch, the improvement comprising intimately mixing finely divided diatomaceous earth with the said suspension, in

n 3 the proportion of not substantially more than 1. part by weight of diatomaceous earth to 1 part of pitch, and then forming paper from the suspension.

12. In making paper from an aqueous sus'pen sion of fibrous material and pitohfthe improvement comprising intimately mixing finely divided diatomaceous earth with the said suspension, in the proportion oi. approximately part by weight of diatomaceous earth to 100- parts of fibrous materiai, and thenjormlng paper from the suspension.

. 13. A sheet of printing paper comprising felted organic fibrous material and a filling material consisting of finely divided diatomaceous earth.

CARLTON J. ONEIL. 

